Data storage systems are arrangements of hardware and software that include one or more storage processors coupled to arrays of non-volatile storage devices, such as magnetic disk drives, electronic flash drives, and/or optical drives, for example. The storage processors service storage requests, arriving from host machines (“hosts”), which specify files or other data elements to be written, read, created, or deleted, for example. Software running on the storage processors manages incoming storage requests and performs various data processing tasks to organize and secure the data elements stored on the non-volatile storage devices.
Data storage systems are sometimes deployed across two geographical sites, with the two sites acting as mirrors to each other and storing the same data. For example, IO (Input/Output) requests specifying writes to a data storage system at a first site may be mirrored to a data storage system at a second site, such that the same writes are performed at both sites. Some arrangements may support reading and writing from both sites, in a so-called “active-active” arrangement, with communication protocols maintaining consistency and coherence between sites. A well-known system for supporting active-active data access over distance is the VPLEX family of storage systems, available from EMC Corporation of Hopkinton, Mass.